This disclosure relates generally to the field of cryocoolers and, more specifically, to the construction and arrangement of a linear cryocooler.
For certain applications, such as space infrared sensor systems, a cryogenic cooling subsystem is required to achieve improved sensor performance. Numerous types of cryogenic cooling subsystems are known in the art, each having a relatively strong attributes relative to the other types. Stirling and pulse-tube linear cryocoolers are typically used to cool various sensors and focal plane array in military, commercial and laboratory applications. Both type of cryocoolers use a linear-oscillating compressor to convert electrical power to thermodynamic pressure-volume (PV).
A conventional reciprocating cryogenic refrigerator, such as a Stirling-cycle cryocooler, has a single working volume that is utilized by both a compressor and displacer. The most common implementation features physically distinct compressor and displacer subassemblies, which may be mounted within a single housing or split into two modules connected by a transfer line. Another approach is to concentrically arrange the compressor and displacer movable parts. One of the parts may be a cylindrical piston, a portion of which moves within a central bore or opening in a cylinder that is the other moving part. The piston may be a component of the compressor and the cylinder, a component of the displacer, or vice versa. The dynamic working volume, which is that portion of the working volume that is varied based upon the motion of the moveable parts, is located, in part, in a bore of the cylinder, between the piston and a regenerator that is coupled to the moveable cylinder. Additional dynamic working volume is located at the end of the Stirling displacer. Movement of either the piston or the cylinder can cause compression or expansion of the working gas in either or both of the dynamic volumes. Proper phasing of these expansion and compression processes between the volumes is what generates refrigeration. Seals (tight clearance gap, sliding, etc.) are maintained between the piston, the cylinder, and the fixed housing that contains them to minimize leakage between the working gas and the plenum gas while still allowing for free movement of the piston and the cylinder. The arrangement in which the compressor and the displacer are concentric to each other allows for placement of these mechanisms into a single, compact housing, which in turn reduces the size and mass of the cryocooler in comparison to a two-module design.
However, these conventional approaches often involve difficult thermal paths from the compression chamber to a heat sink to complete the thermodynamic cycle, resulting in reduced thermodynamic efficiency and potential catastrophic failure due to thermal expansion induced contact between moving surfaces.
What is needed is a thermal-cycle cryocooler with an improved thermal path and increased thermodynamic efficiency that overcomes the above-identified deficiencies.